Radio frequency (RF) power amplifier assemblies are known to include a power amplifier circuit, a cover, and a chassis that contains a heat sink. The power amplifier circuit typically includes multiple known amplifier circuits, DC distribution circuitry, and peripheral circuitry, such as a lowpass filter, a directional coupler, and an isolator. The circuit elements of the power amplifier are attached to the heat sink via screws or other equivalent fasteners, to accommodate the extraction of heat from the circuit elements to the heat sink during operation. The cover is attached to the chassis and encloses the power amplifier circuit to provide environmental and electromagnetic shielding of the enclosed circuitry. When a low level input signal is provided to the input of the power amplifier assembly, the power amplifier circuit amplifies the input signal to a predetermined output level and provides the amplified signal to the power amplifier assembly's output.
Since the power amplifier assembly is inherently inefficient, a significant amount of heat is generated by the power amplifier circuit during amplification of the input signal. Efficiencies of high power RF power amplifier assemblies (i.e. assemblies which provide over twenty-five watts of output power) are generally limited to a range of twenty to fifty percent due to the limitations of present technology. Thus, in power amplifier assemblies that provide several hundred watts of RF output power, as is often the case with power amplifier assemblies incorporated in paging transmitters, heat sink power dissipations of over one kilowatt are commonplace.
Prior art techniques have provided a variety of solutions to the dissipation dilemma. One approach utilizes a cast heat sink that occupies a volume of over 0.08 cubic meters and weighs approximately eighty pounds to dissipate one thousand five hundred watts while providing approximately three hundred watts of RF output power. Another approach, as detailed in U.S. Pat. No. 4,963,833, substantially reduces the weight of the power amplifier assembly by using heat pipe technology. However, none of the prior art solutions, with one kilowatt heat sink dissipation capabilities, provide compatibility with the current market's desire for modularity in base station, or repeater, designs due to their large sizes and unique mechanics.
Therefore, a need exists for a power amplifier assembly that occupies substantially less volume than prior art assemblies that dissipates at least one kilowatt, that is compatible with modular designs, and that utilizes preferred heat sink technology.